Test & document SKIP in generator constructor

Closes #1593

docs/generators.md

@@ -221,3 +221,21 @@ For full example of implementing your own generator, look into Catch2's
 examples, specifically
 [Generators: Create your own generator](../examples/300-Gen-OwnGenerator.cpp).
 
+
+### Handling empty generators
+
+The generator interface assumes that a generator always has at least one
+element. This is not always true, e.g. if the generator depends on an external
+datafile, the file might be missing.
+
+There are two ways to handle this, depending on whether you want this
+to be an error or not.
+
+ * If empty generator **is** an error, throw an exception in constructor.
+ * If empty generator **is not** an error, use the [`SKIP`](skipping-passing-failing.md#skipping-test-cases-at-runtime) in constructor.
+
+
+
+---
+
+[Home](Readme.md#top)

docs/skipping-passing-failing.md

@@ -84,6 +84,12 @@ exit code, same as it does if no test cases have run. This behaviour can
 be overridden using the [--allow-running-no-tests](command-line.md#no-tests-override)
 flag.
 
+### `SKIP` inside generators
+
+You can also use the `SKIP` macro inside generator's constructor to handle
+cases where the generator is empty, but you do not want to fail the test
+case.
+
 
 ## Passing and failing test cases